Load-bearing structures with overlapping edges which are fitted together or otherwise combined to make a load-bearing surface, are well known. Illustrative are hard wood flooring pieces provided with tongue and groove interfit. Nevertheless, there is a need for a load-bearing structure having an improved interlocking edge, and in particular with reduced weight but yet good load-bearing properties.
Thermoplastic polymer/reinforcing fiber composites are used to replace metals in aerospace and automotive applications. However, new applications have been slow due to the higher cost of composites when compared to conventional materials like metal, wood or concrete. If the cost could be adequately reduced and yet the strength could be maintained, numerous applications exist where thermoplastic polymer/reinforcing fiber composites could replace metal, wood or concrete. These applications include furniture framing, power poles, shipping containers, crates, shipping pallets, platforms, construction decking, bridge decking, mud pads, road mats, driveways, warehouse flooring, and flooring for trucks and trailers.
Known uses of thermoplastic polymer/reinforcing fiber composites further include reinforcing bars or re-bars, reinforced mats and reinforced fabrics. These uses are illustrated in U.S. Pat. No. 4,154,634 to Shobert et al, U.S. Pat. No. 4,752,513 to Rau et al, and U.S. Pat. No. 5,190,809 to Marissen et al. Advantageously, the thermoplastic polymer strengthens and stiffens the composite. This type of polymer is often termed a "matrix resin" in the context of polymer/reinforcing fiber composites.
Engineering type, plastic resins such as polyester, nylon, polyphenylene sulfide and polyurethane are frequently used as matrix resins in fiberglass composite laminates and pultrusion profiles. When solid, these resins are very rigid and provide the most stiffness, but fracture when overstressed, often leaving sharp splintered edges.
Accordingly, there is a need for load-bearing structures of reduced cost and yet good load-bearing properties. In addition, if fiber/matrix resin composites are used in certain load-bearing structures, there is a need for flexibility of the composites so that fracturing and sharp splintered edges do not result.